《C#数据库开发经典案例解析》光盘源码 可以参考-" C# Database Development classic case analysis" can refer to CD-ROM Source

从Point、Circle类中抽象出基类Shape，研究抽象类和具体类的接口和实现。-Abstracts the base class from Point and Circle Shape, the abstract class and interface and implementation of a concrete class.